Corner reflectors (also known as "corner cubes") are well known reflective devices. As shown in FIG. 1A, a light ray incident upon a corner reflector undergoes total internal reflection in each of three separate reflections at the three perpendicularly opposed facets which form the corner, with the net result that the light is retro-reflected from the corner reflector in a direction opposite to the direction of the incident ray.
Miniaturized transparent groupings of corner reflectors, each of which reflectors exhibit the above-described phenomenon of total internal reflection, are commonly found in reflective sheeting materials such as 3M Diamond Grade.TM. reflective sheeting. If the total internal reflection phenomenon could be switched on or off for a group of one or more corner reflectors, then that group could function as an image "pixel". An array of such pixels could then be assembled to construct a display device capable of displaying text or images. The present invention achieves this.
The prior art has evolved a variety of reflective image display devices. Examples include non-backlit liquid crystal display ("LCD") panels like those commonly used in calculators, and "flip" signs of the type used in some buses to display route information. However such devices are subject to various shortcomings. For example, LCD panels typically exhibit less than 50% maximum reflectivity, due to the required front polarizer. Flip signs are mechanically complex and it is difficult to miniaturize the pixels. The present invention is not subject to the same shortcomings.